1. Field of the Invention
This invention relates to a method and apparatus for treating a sludgy substance, namely a liquid containing therein suspended solids, for thereby separating from the liquid the suspended solids in a concentrated dewatered state. More particularly, this invention relates to a method and apparatus for separating suspended solids in a concentrated, dewatered state from a liquid, therein organic or inorganic suspended solids such as activated sludge, excess sludge and sedimented sludge originating in water and wastewater treatment facilities, and which can also be used for recovering proteins from the effluent which issue from food processing plants specializing in the production of fish meat pastes or for separating squeezed juice from fruit pulp in plants specializing in the production of fruit juice.
2. Description of the Prior Art
For the treatment of solids-containing liquids aimed at separating the solids in a concentrated, dewatered state as described above, there have heretofore been adopted various devices including filter presses, traveling filter cloth type dehydraters and vacuum filters. All the devices known in the art have invariably used filter cloths for the purpose of solid-liquid separation. Filter cloths have a disadvantage in that they clog when used continuously and consequently become degraded in their treating ability. They are also apt to break easily while in use.
Japanese Patent Public Disclosure No. 28967/1974 discloses a continuous exuding device which comprises two laterally opposed trains each consisting of a plurality of rotary filter elements which are each formed of a multiplicity of circular plates arranged face to face in the axial direction at fixed intervals and which are so disposed that they intermesh so as to permit the circular plates of each rotary filter element partially to enter the corresponding spaces between the circular plates of the immediately adjacent rotary filter element, which apparatus is operated by causing a sludgy substance to be fed under pressure into the passage intervening between the trains of rotary filter elements for thereby allowing the substance to be exuded by the opposed trains approaching each other in the direction from the inlet to the outlet and, at the same time, to be conveyed toward the outlet by the individual rotary filter elements being rotated around their shafts. This exuding device, however, exhibits insufficient treating ability when used on a feed liquid such as slurry containing much water because the water component separated from the solid component is discharged only through the portions in which the circular plates of one rotary filter element partly enter the spaces intervening between the circular plates of the immediately adjacent rotary filter element.
Generally this device has insufficient treating ability because the liquid under treatment is allowed to come into contact with only half of the surfaces of the rotary filter elements, namely only half of the whole portions of the rotary filter elements take part in the filtration of the liquid under treatment. This device has another disadvantage that it fails to produce a sufficiently dehydrated cake because the rotary filter elements in each train are so arranged as to be rotated at circumferential speeds gradually increasing with the decreasing distances of the relevant rotary filter elements from the outlet.
An object of the present invention is to provide a method and apparatus capable of effectively dewatering a sludgy substance without requiring use of easily clogging materials such as filter cloths.
Another object of the present invention is to provide a method and apparatus for dewatering a sludgy substance, which permits efficient separation of a sludgy substance into clear liquid and a cake containing filter water.